1. Field of the Invention
The present invention relates to an optical burst switching (OBS) network, and more particularly, to a method of reducing a transmission error of burst data (BD) in an OBS network.
2. Description of the Related Art
In general, an electrical switch is used to transmit and/or receive an optical signal through an optical fiber or a link. However, the electrical switch must convert the optical signal into an electric signal and the electric signal into the optical signal in order to process the received optical signal. Thus, a network that uses an electrical switch additionally requires an opto-electric converter to convert an optical signal into an electric signal and an electro-optic converter to convert an electric signal into an optical signal. As a consequence, cost of the network implementation is increased.
To solve this problem, optical burst switching has been suggested, which immediately processes a received optical signal without converting the optical signal into an electric signal. An OBS network using such optical burst switching will now be described.
In general, in an OBS network, IP packets that are input into an optical domain are collected as BD by an edge node. The BD passes through a core node, is routed, and is then transmitted to a destination node depending on destinations of the BD or Quality of Service (QoS). Also, a burst control packet (BCP) and the BD are separated from each other by an offset time and then transmitted using different channels. In other words, the BCP is transmitted prior to the BD by the offset time to reserve a path through which the BD is to be transmitted, which provides rapid transmission of the BD through the optical network without the BD being buffered. A process of transmitting optical data will now be described with reference to FIG. 1.
FIG. 1 illustrates nodes that transmit or receive the BD and nodes that switch the BD in an OBS network. A process of transmitting BD in an OBS network will now be described.
A node 100 is an edge node receiving and collecting IP packets to make BD. Edge nodes 100, 106, and 108 collect IP packets to create and transmit optical burst data packets or receive optical burst data packets to separate IP packets from the optical burst data packets. Core nodes 102 and 104 optically switch optical burst data. If BD having a desired size is generated, node 100 generates a BCP, transmits the BCP to core node 102, and transmits the BD to node 102 after an offset time. The BCP includes information of a destination address and a generation address of the BD, a size of the BD, a QoS offset time, and the like.
Node 102 checks a destination address of BD to be received after the BCP and node 102 determines an optical path using the BCP so as to reserve an optical switching time. The BCP is opto-electric converted and/or electro-optic converted in node 102, but the BD goes along the optical path only by optical switching without opto-electric conversion of the BD. Node 102 may optically switch the BD to node 106 or 104 depending on whether a destination of the BD transmitted from node 100 is node 106 or 108.
BD may be transmitted from node 100 to node 102 and then transmitted to node 106 or 108. However, node 102 may be a destination of BD generated by node 100 or node 102 may directly generate BD to be transmitted to node 106 or 108. In other words, node 100 that is a core node may have a function of an edge node.
However, in a case of a node B, destinations of BD transmitted from a node A and BD transmitted from a node C may be a node D. In this case, the node B may not transmit the BD to the node D at a point of time. Thus, the node B selects one piece of the BD and first transmits the selected BD piece. Also, unselected pieces of the BD may be delayed for a predetermined period of time and then transmitted. Thus, data loss may be prevented.
However, the OBS network does not have a buffering function. Thus, in a case where the OBS network receives a plurality of pieces of BD, the OBS network may not efficiently process the BD.